This invention relates to a wireless telephone system for employing one or a plurality of orbiting satellites to allow wireless telephone users (subscribers) communication access to a terrestrial telephone system (whether private, government or common carrier), and particularly to a wireless telephone system, such as a cellular system, which permits subscriber access to terrestrial telephone networks while the subscriber is roaming in areas that do not have cellular telephone services.
There is a need to provide personal communications anywhere on the earth. Current communications systems, for example, cellular telephone systems, require terrestrial cellular relay stations to intercept and link a cellular radiotelephone transmission with conventional switched telephone users and with other cellular telephone users. All of the existing communications systems have limited user range.
Cellular telephone systems have been proposed which account for roamers, i.e., cellular telephone users which roam outside a normal service area. The American Telephone and Telegraph Corp. (AT&T) has proposed an inter-cellular data network for interconnecting terrestrial cellular telephone service areas using a terrestrial packet-switched network that has nodes at the participating cellular telephone service areas wherein packet-switched network data are accumulated in a database of roaming cellular telephone users. The database therein proposed would keep track of roamers and allow terrestrial interconnection of the roamer to the telephone system when the roamer is located in a cellular telephone service area that is remote from a designated home cell. Certain data are collected which would allow routing of calls to the roaming user, allow issuance of billing information, and allow collection of other system operation data.
Efforts are under way to utilize satellite technology in cellular communications. Satellite delivered telephone services to mobile users have been proposed as the Mobile Satellite System (MSS) in the USA. This system is now being implemented by the American Mobile Satellite Corp. (AMSC). It utilizes transceivers in the mobile unit (automobile for example) operating in the L-band (1530-1560 MHz and 1646.5-1660.5 MHz) that communicate to a satellite at geosynchronous orbit. This system is limited to serving just a small portion of the earth. In addition to significant expense to the end user for the transceiver apparatus, the system is subject to noticeable relay delay due to transmission of the signals to and from geosynchronous orbit. Furthermore, the cellular telephone service providers must nevertheless implement a costly additional inter-system network to direct calls to the mobile transceiver apparatus. The current system as envisaged does not have a method for locating the roaming user and directing the call to the user.
U.S. Pat. No. 4,972,456, assigned to GTE MobileNet, discloses a cellular telephone "satellite" roaming system that uses a satellite system to permit access to the cellular telephone system when a user is located in areas outside of cellular telephone system coverage. This system does not contemplate overhead orbiting satellites, but rather the system would employ subsidiary cell sites in a terrestrial-based cellular communications system.
Other patents relate to general information on cellular telephone roaming systems which permit a user of one cellular system to use another cellular system while traveling in areas outside a home cellular system. These patents include U.S. Pat. Nos. 4,901,340; 4,972,460; and 4,833,701.
Motorola, Inc. announced on Jun. 27, 1990 a proposed crosslinked satellite network under the name IRIDIUM. The IRIDIUM system is believed to be described in European Patent Publication EP 365,885, published May 2, 1990, and corresponding to U.S. patent application Ser. No. 263,849 filed 28 Oct. 1988. The IRIDIUM system envisions a constellation of seventy-seven low-earth orbiting satellites in seven circular polar orbits for supporting cellular telephone communications on the earth's surface. In the IRIDIUM system, all handoff and relays of communications traffic are handled in space directly between satellites, so that the terrestrial telephone network is bypassed. However, ground signal processing is required to set up and place calls. Calls originating from outside the satellite service areas must interrogate the home location of the user in order to identify the user. The system requires that all satellites be linked constantly to one another. Each of eleven evenly-spaced satellites sharing an orbit plane is contemplated to project thirty-seven communications cells on the earth's surface. Additionally, each satellite has four intersatellite links, thus forming a geodesic sphere for traffic communication paths. Due to cost and channel limitation, it may be presumed that the IRIDIUM system will not compete with the services provided by terrestrial-based cellular communications systems. A technical description of this invention is believed to be contained under U.S. patent application Ser. No. 263,849 filed Oct. 28, 1988 in the names of Bertiger, Leopold and Peterson.
By a document dated Nov. 2, 1990, Ellipsat Corporation made application to the Federal Communications Commission for authority to construct an elliptical orbit satellite system to support, among other things, mobile voice services in the United States through a constellation of six satellites. The service has been presented as complementary of and not competitive with existing and future (terrestrial) cellular telephone services. The system contemplates the use by end users of dual-mode transceivers using Code Division Multiple Access (CDMA) modulation to effect communications with earth satellites in extended-coverage elliptical orbit.